Heretofore, for example, in an automated assembly line for automobiles, an assembly process has been carried out in which clamping is performed by a clamp apparatus under a condition in which pre-formed frames are positioned in an overlaid manner and the frames are welded together.
As one clamp apparatus of this type, for example, as disclosed in Japanese Patent No. 4950123, the clamp apparatus comprises a pair of clamp arms, the clamp arms being disposed on left and right sides and supported pivotally by pins, and an air cylinder that generates a driving force for rotating the clamp arms. By supplying a pressure fluid to the air cylinder, the driving force is transmitted to the clamp arms through a base connected to the end of a piston rod. By rotation of the clamp arms respectively through the pins, distal ends of the clamp arms are operated to open and close, to thereby grip a workpiece such as a frame or the like from left and right sides thereof.